1. Field of the Invention
The present invention relates to an electronic control of the operation run of a vehicle and, more particularly, to a revolution signal processing system of the self-testing, backup-type for self-testing revolution signals of the electronic controller and for backing up the same during malfunctions.
2. Description of the Prior Art
When a vehicle, such as an automobile, is to have its gear position changed automatically, this shifting operation is effected wholly electrically in the prior art, when an electronic signal processing system is used. By turning on or off one or more switches, therefore, it is feasible to set several speed changing patterns for effecting economical operation, sporty performance and so on. Since detections of signals and computations of speed changing points are usually accurate, moreover, dispersion of the gear shifting points is reduced to shorten delay in the timing for the speed change. Thanks to its independence, moreover, the electronic controller has an advantage that it can be maintained easily without any restriction from other controllers. Thus, the automatic transmission using the electronic controller of the above-specified type has a tendency to be more widely used each year.
Although this automatic transmission has the various advantages, its self-test and backup capabilities are problems. Specifically, when the gear position is to be determined by using signals which are outputted from a vehicle speed sensor and an input shaft revolution sensor, the vehicle speed exhibits a value of zero despite the vehicle running, if the vehicle speed sensor or the input shaft revolution sensor is malfunctioning, e.g. it is broken or has its circuit shorted or disconnected. With the vehicle speed at zero, the automatic gear shift does not perform. If the circuit is broken during high-speed operation, on the other hand, the gear is shifted down to a first speed, resulting in the danger that the engine may over run.